1. Field of the Invention
The present invention relates to a blood pump, which used as a cardiac assist device. More particularly, this invention relates to a blood pump, which is free from leakage of blood from the pump chamber and occurrence of hemolysis and clotting in use.
2. Prior Art
There have been known blood pumps, which comprise a pump chamber provided with a blood inlet port at the top thereof and a blood outlet port provided in the direction perpendicular to the axis of the blood inlet port and an impeller which comprises a base plate (hub) and blades provided on the base plate generally uprightly and generally radially and is secured to a rotation shaft and rotatably installed in the pump chamber.
In blood pumps of this type, the blood introduced through the inlet port is discharged through the outlet port by the rotation of the impeller.
In blood pumps of this type, the sealing between the rotation shaft of the impeller and the rotation shaft hole provided in the bottom of the pump chamber is effected with a mechanical means. As a result, the high speed rotation of the impeller generates heat because of the friction between the seal member and the rotation shaft or the surface of the pump chamber bottom depending on the structure. The frictional heat may promote hemolysis or cause clotting. Therefore, blood pumps of this type have defect that they cannot bear prolonged operation.
A clotting-prevention type blood pump, which is intended to solve the above problem, is disclosed in Japanese Laid-Open Patent Publication No. Sho 61-500058, which corresponds to PCT application.
In this clotting-prevention type blood pump, the bearing, which rotatably supports the impeller shaft positioned in the impeller chamber, is constructed hydrodynamically. That is, through the clearance between the rotation shaft and the surrounding supporting section, a pressurized sealing fluid penetrates into the impeller chamber. By the penetration of the fluid into the impeller chamber, prevention of leakage of blood out of the impeller chamber is intended.
In this cloting-prevention type blood pump, however, if the pressure in the impeller chamber and the pressure of the sealing fluid are inverted, or if the sealing fluid is not sufficiently supplied, blood will leak through said clearance. This means that the sealing is not only impaired but the leaking blood may clot in the impeller mechanism, which will hinder smooth rotation of the impeller and thus make difficult the continuous normal operation of the blood pump. Thus problems troublesome for the blood pump such as hemolysis and thrombosis are caused.
The present invention was made to solve the above-described problems. That is, it is the object of the present invention to provide a blood pump which can normally operate even when the pressure in the pump chamber (impeller chamber) and the pressure of sealing liquid are inverted and is free from occurrence of hemolysis and thrombosis.